The principal goal of this project is to examine alpha- and beta-adrenergic receptors in two catecholamine-responsive cell lines--Madin Darby Canine Kidney (MDCK) and BC3H-1 muscle cells. These 2 cell types are unique because they each co-express both alpha1-adrenergic and beta2-adrenergic receptors. Data obtained thus far in these systems indicate that the 2 receptors are discrete entities which possess different functional responses, binding properties, and second messengers and which may be independently regulated. Aspects of the receptors that we will examine in the current proposal include interaction of agonists with receptors on intact cells (in which we will test for differences in early events by which the cells "process" alpha and beta receptors), transmembrane signalling by alpha1-receptors in MDCK cells (in particular, a novel guanine nucleotide binding protein that links alpha1-receptors to cellular response systems and the relationship between phosphoinositide hydrolysis and arachidonic acid release/prostaglandin E2 generation), and cellular and molecular mechanisms that mediate homologous desensitization and a new form of desensitization ("crossed" desensitization of beta2-adrenergic response by alpha1-adrenergic receptors). Additional efforts will be directed at generating variant clones having lesions in the pathway of alpha-adrenergic response in these systems. The results should provide new insight into the regulation of mammalian cells that can respond to catecholamines. The results should be of particular relevance to hypertension and other diseases that involve adrenergic response in smooth muscle and kidney.